I get what you are saying, however I feel there are two major things you are skipping over.
1: NPC's as it is currently, do not act appropriately to player created situations, it stands to reason if some pirates decide to blockade a system they would be blown out of the sky by system defense forces, (depending on the security level of the system naturally), so players being able to blockade any system they 'want' to blockade makes no sense, now if a player group had worked hard to reduce the security of the system down to a point where it is near anarchy then sure then it would be possible because the system defence forces would be near non existing. But this is one of the major problems I see with people wanting to be pirates and able to control a system, they do not want npc's to do anything about it. They only want things to go 'their' way to be able to blockade and force traders away from possible lucrative routes. And that seems so lopsided that it is not funny.
2: The P2P nature of the game, lets say that a group of american's from the westcoast want to blockade a system, and there are traders from Europe or such that want to use it, assuming ALL players involved have a perfect latency that still leaves around 150-200 ms, in a shooter game, that can be tricky, though not unmanageable. However as I'm sure we all are aware off, perfect latency is not the standard, and it would become a laggy mess with the clients trying to decide who is right and who is not, a solution would be a server deciding such things hybrid p2p, which might work.